NDUFA12 as a Functional Target of the Anticancer Compound Ertredin in Human Hepatoma Cells As Revealed by Label-Free Chemical Proteomics

Many attempts have been made to develop new agents that target EGFR mutants or regulate downstream factors in various cancers. Cell-based screening showed that a natural small molecule, Ertredin, inhibited the growth of EGFRvIII mutant cancer cells. Previous studies have shown that Ertredin effectively inhibits anchorage-independent 3D growth of sphere-forming cells transfected with EGFRvIII mutant cDNA. However, the underlying mechanism remains unclear. In this study, we investigated the target protein of Ertredin by combining drug affinity-responsive target stability (DARTS) assays with liquid chromatography-mass spectrometry using label-free Ertredin as a bait and HepG2 cell lysates as a proteome pool. NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 12 (NDUFA12) was identified as an Ertredin-binding protein that was responsible for its biological activity. The interaction between NDUFA12 and Ertredin was validated by DARTS and cellular thermal shift assays. In addition, the genetic knockdown of the identified target, NDUFA12, was shown to suppress cell proliferation. NDUFA12 was identified as a biologically relevant target protein of Ertredin that is responsible for its antitumor activity, and these results provide insights into the role of NDUFA12 as a downstream factor in EGFRvIII mutants.

New anti-cancer chemicals Ertredin and its derivatives, regulate oxidative phosphorylation and glycolysis and suppress sphere formation in vitro and tumor growth in EGFRvIII-transformed cells

BACKGROUND

EGFRvIII is a mutant form of the epidermal growth factor receptor gene (EGFR) that lacks exons 2-7. The resulting protein does not bind to ligands and is constitutively activated. The expression of EGFRvIII is likely confined to various types of cancer, particularly glioblastomas. Although an anti-EGFRvIII vaccine is of great interest, low-molecular-weight substances are needed to obtain better therapeutic efficacy. Thus, the purpose of this study is to identify low molecular weight substances that can suppress EGFRvIII-dependent transformation.

METHODS

We constructed a new throughput screening system and searched for substances that decreased cell survival of NIH3T3/EGFRvIII spheres under 3-dimensional (3D)-culture conditions, but retained normal NIH3T3 cell growth under 2D-culture conditions. In vivo activity was examined using a mouse transplantation model, and derivatives were chemically synthesized. Functional characterization of the candidate molecules was investigated using an EGFR kinase assay, immunoprecipitation, western blotting, microarray analysis, quantitative polymerase chain reaction analysis, and measurement of lactate and ATP synthesis.

RESULTS

In the course of screening 30,000 substances, a reagent, "Ertredin" was found to inhibit anchorage-independent 3D growth of sphere-forming cells transfected with EGFRvIII cDNA. Ertredin also inhibited sphere formation in cells expressing wild-type EGFR in the presence of EGF. However, it did not affect anchorage-dependent 2D growth of parental NIH3T3 cells. The 3D-growth-inhibitory activity of some derivatives, including those with new structures, was similar to Ertredin. Furthermore, we demonstrated that Ertredin suppressed tumor growth in an allograft transplantation mouse model injected with EGFRvIII- or wild-type EGFR-expressing cells; a clear toxicity to host animals was not observed. Functional characterization of Ertredin in cells expressing EGFRvIII indicated that it stimulated EGFRvIII ubiquitination, suppressed both oxidative phosphorylation and glycolysis under 3D conditions, and promoted cell apoptosis.

CONCLUSION

We developed a high throughput screening method based on anchorage-independent sphere formation induced by EGFRvIII-dependent transformation. In the course of screening, we identified Ertredin, which inhibited anchorage-independent 3D growth and tumor formation in nude mice. Functional analysis suggests that Ertredin suppresses both mitochondrial oxidative phosphorylation and cytosolic glycolysis in addition to promoting EGFRvIII degradation, and stimulates apoptosis in sphere-forming, EGFRvIII-overexpressing cells.